Gas turbines generally include a turbine rotor (wheel) with a number of circumferentially spaced buckets (blades). The buckets generally may include an airfoil, a platform, a shank, a dovetail, and other elements. The dovetail of each bucket is positioned within the turbine rotor and secured therein. The airfoils project into the hot gas path so as to convert the kinetic energy of the gas into rotational mechanical energy. A number of cooling medium passages may extend radially through the bucket to direct an inward and/or an outward flow of the cooling medium therethrough.
Leaks may develop in the coolant supply circuit based upon a gap between the tabs of the dovetails and the surface of the rotor due to increases in thermal and or centrifugal loads. Air losses from the bucket supply circuit into the wheel space may be significant with respect to blade cooling medium flow requirements. Moreover, the air may be extracted from later compressor stages such that the penalty on energy output and overall efficiency may be significant during engine operation.
Efforts have been made to limit this leak. For example, one method involves depositing aluminum on a dovetail tab so as to fill the gap at least partially. Specifically, a circular ring may be pressed against the forward side of the dovetail face. Although this design seals well and is durable, the design cannot be easily disassembled and replaced in the field. Rather, these rings may only be disassembled when the entire rotor is disassembled.
Other known methods include those described in commonly owned Ser. No. 12/168,297, filed herewith, entitled “Gas Turbine Seal”; Ser. No. 12/168,932, also filed herewith, entitled “Labyrinth Seal for Turbine Dovetail”; and similar types of dovetail seals and methods. These seals and methods generally may use a sealing slot positioned about a tab of a dovetail. These slots, however, can be difficult to manufacture and may require non-conventional machining processes. Current methods may include EDM (Electrical Discharge Machining), keyway cutting, end milling, or hybrid processes.
There is thus a desire for improved dovetail tab sealing systems and methods. Such systems and methods should provide a substantially uniform sealing slot without the use of the non-conventional machining processes. Such a substantially uniform sealing slot may be used with a number of different seals and methods so as to adequately prevent leakage therethrough and to increase overall system efficiency.